The present invention relates to balloon catheters in general and, more particularly, to methods for forming low profile balloons for catheters.
Balloon catheters have found widespread use for treating a variety of vascular diseases. Typically, a physician guides the catheter with a balloon thereon through a patient""s vascular system and positions the balloon across a stenosis. The balloon is then inflated, stretching the vessel and/or pressing the lesion into the vessel wall to re-establish blood flow through the vessel. To treat a very tight stenosis with small opening, a low profile catheter and balloon that can fit through and across the stenosis is required. A low profile also improves the ability to navigate the catheter through tortuous vascular structures.
FIG. 1 illustrates a typical balloon catheter assembly in a pre-inflated state. The balloon catheter assembly 10 shown comprises an inner shaft 20 placed coaxially within an outer shaft 30, and a balloon 40 affixed co-axially over the inner and the outer shafts. The balloon 40 has a balloon region 42 interposed between a proximal portion 44 and a distal portion 46. The proximal portion 44 of the balloon is sealingly attached with the outer shaft 30 and the distal portion 46 with the inner shaft 20, with the balloon region 42 being folded or wrapped about the inner shaft.
The balloon 40 typically is formed of a continuous, flexible piece of non-elastomeric polymeric material. One balloon forming technique, known as balloon blowing, involves providing a polymeric tube and expanding a region of the polymeric tube under pressure to form the balloon region of the balloon. To narrow the proximal and the distal portions of the balloon, the end portions of the polymeric tube that will become the proximal and the distal portions of the balloon are xe2x80x9cneckedxe2x80x9d, or stretched, while the region of the polymeric tube that will form the balloon region of the balloon is kept the same. Necking reduces both the inner and the outer diameters of the end portions while simultaneously elongating the end portions of the polymeric tube.
Necking has its limits, however. On a molecular level, necking causes the polymer molecules to orient. As the end portions are stretched more and more, the outer diameter of the end portions become narrower and narrower, and the polymer molecules become more and more oriented. At some point, the polymer molecules will become so oriented that the end portions of the polymeric tube lose their flexibility, and can be stretched no further and will break instead. At this point, the polymeric tube is no longer useful for forming into a balloon. Necking alone often can not reduce the outer diameter of the proximal and the distal portions of the balloon sufficiently to produce a low profile catheter capable of maneuvering through very tight vascular structures or through very tight stenoses.
The present invention describes methods of forming a low profile balloon that can be used with a catheter. The methods involve providing a polymeric tube, removing material from the outer surface of the polymeric tube around at least one of the end portions of the polymeric tube, and inflating a region of the polymeric tube to form the balloon. The end portions of the polymeric tube optionally may be necked prior to the removal of material from the outer surface thereof. Material from the outer surface of the polymeric tube may be removed by various means. In one embodiment, the material is removed using a grinding wheel. In another embodiment, the material is removed using a laser. In yet another embodiment, the material is removed using a lathe.